This invention relates to switching power supplies and more particularly to systems with multiple switching regulators drawing current from the same input power source.
Many electronic devices require multiple power supplies. For example, a device with both analog and digital circuits may require +5 volts for the digital logic, and +12 Volts, xe2x88x9212 volts for the analog circuitry. In battery powered devices, switching power supplies are a way to create these power supplies.
A switching power supply may function by having a controller switch a transistor at high frequency. This frequency is typically in the 20 kHz to 1 MHz range. This draws current from the input power source to produce a chopped intermediate voltage that is then filtered by an L-C (inductor-capacitor) circuit to produce a smoother output voltage. The output voltage is controlled by varying the on time to off-time ratio of the transistor. Unfortunately, if there are multiple regulators in the system, the switching transistors of these multiple regulators may switch on and off in phase. This switching in phase can causes multiple regulators to be drawing current at the same time, this increases the current drain on the input power source. In fact, with enough switching transistors switching in phase, the current drain on the input power source may increase to the point where regulation cannot be maintained. Due to the high series resistance of many types of batteries, battery powered devices are particularly susceptible to this condition.
Accordingly, there is a need in the art for a multiple voltage switching power supply controller that helps lower the peak current drain on the input power source.
The invention coordinates the current drawn by multiple switching regulators sharing a common input power source to lower the peak current drain on the input power source. Coordination of the current drawn can be implemented with simple logic, or can be adapted to a complicated algorithm that takes into account many different variables such as dynamic loading of different regulators or worst case scenarios. One embodiment sequences the turn-on, turn-off, or intermediate switching times of the switches in each regulator so that each regulator draws current at a predetermined time in a cycle. The predetermined time for each regulator is chosen so that the maximum peak current drain on the input power source is minimized. The predetermined times may be changed on-the-fly by inputs to the system when information about current or projected output loads are known. Another embodiment merely sequences the turn-on or turn-off times of the switches in each regulator so that each regulator starts drawing current when the previous regulator in the sequence stops drawing current. Another embodiment lets the regulator with the largest change in input current over a cycle run independently. The other regulators then draw current in a designated order or at designated times after the first regulator turn stops drawing current.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.